Safety relief valve



June 8, 1954 E. A. PRIJATEL 2,680,453

SAFETY RELIEF VALVE Filed April 13, 1950 Patented June 8, .1.954

2,680,453 SAFETY RELIEF VALVE Edward Anthony Prijatel assignor to Borg-Warn l., a corporation of Illinois Application April 13, 1950, Serial No.

South Euclid, Ohio, er Corporation,

Chicago,

3 Claims. A (Cl. 137-490) This invention relates to a relief valve for a hydraulic system and more particularly to an employed to hold the relief valve closed.

Relief valves as ordinarily constructed are when the spring pressure is overcome by the total pressure against the Valve, the Valve opens. As pointed out in to different desired relief An object of the present invention is to provide a new and improved relief valve of the type utilizing the system pressure to hold the valve closed until the relief pressure value is reached.

In accordance with invention, such a valve cordance with this invention.

valve seat lI-a. A primary relief valve I2 is arranged to seat on the valve seat I l-a and thereby to close the passage through the valve from the inlet port 6 to the outlet port 1.

The relief valve I2 has a large, dish-shaped to cause the relief valve l2 end of the valve housing 5. Packing disposed between the flanged head of the retainer cap 23 and the inner edge of the opening 24 prevents leakage oi pressure.

The downwardly extending valve stem |4 of the relief valve |2 is journalled in an upwardly extending sleeve portion 26 of a piston 21 disposed within the lower portion of housing 5. Piston 2l is employed in accordance with this invention to lift the relief valve l2 oilits seat when the desired relief pressure level is reached in the system. The lower terminal end of valve stem |4 rests directly on an inwardly extending shoulder or flange 28 integrally formed at the lower end of the sleeve portion 25 of piston 21 and, thus, upward movement of piston 21 is effective to move upwardly off its seat, the piston flange 28 being held in contact with the lower end of valve stem i4 by a spring l5| described in detail hereinafter. The inwardly extending nange 28 denes at its lower edge a valve seat 29 for the truncated, conical head I6 of the control valve l1. When the control valve |1 is moved downwardly relatively to the valve seat 29, system pressure from the port l is communicated to the under side or" piston 21 through a short, angularly disposed passage 30 in the head of piston 21, the passage 30 communicating at its upper end with a chamber 3|, formed in the head of piston V21, into the upper end of which chamber the lower end of the passage |5 in the relief valve stem opens when control valve |1 is unseated. Control valve l1 is held closed by a control spring 32 until the desired relief pressure level is reached in the system, thus preventing pressure from reaching the under side of piston 21 and preventing unseating of the primary relief valve |2.

Referring particularly to the control valve it will be seen that vvalve |1 has extending downwardly from the head 16 a short intermediate stem portion 33 of substantially smaller crosssection than the lower portion of the valve head I6 and the stem portion 33 has integrally formed therewith at its lower end a substantially larger diameter lower end portion 34 of generally cylindrical configuration. End portion 34 is journalled in an opening 35 formed in the cross portion or head of piston 21 in axial alignment with valve seat 29. The control valve l1 is supported on the upper end or a generally rod-shaped member 36, the cross-sectional area of which is critically selected with reference to the areas of the control valve and the control valve stem to achieve the desired operating characteristics as explained hereinafter. The lower end portion SE-a of member 36 is enlarged as compared with the upper end vportion and the lower end 3S-a is rounded and received in a suitable cup-shaped recess 31 formed in a retainer member 33 having a ,peripheral flange 39 against the under side of which the upper end of the control spring 32 bears. The lower end of control spring 32 bears against a flanged, lower portion 4 |-a of an axially elongated adjusting nut 4|', the body portion 4|-b of which is threaded on the externally threaded upper portion of an adjusting screw 42. Adjusting screw 42 is in turn rotatably mounted in a generally cylindrical or cup-shaped retainer or closure cap 43 threaded into the lower end of a sleeve 44, the upper end or which sleeve is threaded into or otherwise rmly secured to the lower side of the housing. Piston 21 is slidably journalled in the'upper portion of this sleeve or cylinder 44.

Retainer cap 43 has a centrally disposed operi'A ing 45 through which the lower end of adjusting screw 42 extends, while adjusting screw 42 has a iiange 46 formed about the lower mid portion thereof, the under side oi" which ange rests on the upper, inner side of the retaining cap 43 in bearing relation. The terminal end of the adjusting screw 42 is provided with a slot 41 to receive the tip of a screw-driver whereby adjusting screw 43 may be rotated to raise or lower the nut 4|, the periphery of which is keyed to the retainer cap 43 by a pair of oppositely disposed keyways 43 iitting into suitable slots in the hanged portion 4|-a of the nut 4|. Accordingly, since the nut 4| is prevented from turning relatively to the cap 43, rotation of the adjusting screw 42 will cause the nut 4| to be moved upwardly or downwardly, in accordance with the direction or rotation, to increase or reduce the compression on spring 32, and thus to set the value or level at which the control valve |1 may open in response to pressure applied to the upper end thereof.

Referring now to the piston 21, which is slidably journalled in the upper portion oiE the sleeve portion 44 of the housing '5, it will be noted that the under side o the piston is provided with a deep, relatively wide, annular recess 5B in whichv the upper portion of a spring 5| is received, the upper end of spring 5| bearing against the upper end` oi the recess 50, Spring 5| holds piston 21 firmly against the lower end of valve stem |4 at all times. The lower end of spring 5| bears against the upper end of cap 43, being retained in axial alignment therewith by an annular shoulder 52 of relatively narrow cross-section formed about the upper end of the cap 43 on the inner dimension thereof. The spring '5| is selected with reference to the compression force exerted by the spring 23 associated with the primary relief valve l2 and, in combination with control spring 32, exerts a force only slightly less than the oppositely directed pressure exerted by the spring 23 on the relief valve yl2 and the piston 21. In this manner, while the relief valve is initially held seated, the opening of the relief valve is in response primarily to the liuid pressures substantially unaiiected by the several springs, which largely counterbalance each other.

It will be noted that the rod-like member 36 associated with andiorming, in effect, a part of the valve stem of control valve |1 is maintained in yaxial alignment with the control valve stem by a bearing or bushing 53 mounted in a downwardly depending cylindrical or tubular portion 54 of the piston 21, the outer periphery oi the tubular portion 54 defining the radially inner side of :the recess 5|) formed in the under side of piston `27| and the yinner side of the downwardly depending portion -54 defining a'chamber 55 communicating at its upper end with the aperture 35 in which the enlarged, lower end 34 oi the valve stem o the control valve |1 is journalled. Bushing `53 serves both as a journal bearing surface for the upper portion of stem member 35 and also as a packing retainermember, the bushing 53 having a groove 56 formed about the periphery ythereoi in which an O-ring :57| is disposed and retained. The upper end of the bushing .53 seats against an inwardly .extending shoulder El! integrally formed with the inner side oi the downwardly depending portion v54 of the piston 2.1 and the bushing is retained in its 4position by .a split ring 6| mounted -in a suitably located groove 62 formed on the inner side of the lower end of piston por' tion 54.

` tion 54 of piston portion of stem lower surface of 21. ber 55 is vented to low pressure.

In order to prevent pressure below the piston 21 resulting from the opening of the control valve and the system pressure could then rise again to the predetermined cracking pressure.

The exposed area of the underside of the piston 6, orice must necessarily be made of small diameter to prevent While but has been shown and described, it will be underto prevent communication between said ports,

a piston connection with said relief valve and eifective in response to. application of system pressure to a motive surface thereof to open said relief valve, a control valve exposed to system pressure for controlling application of system pressure to said piston, said control valve being movable to, open position to, apply system pressure to said piston, said control valve including a stem portion and a separate stern member bearing against an end of said stem portion, a iirst pressure responsiveI surface being defined by the control valve portion exposed to system pressure, a second pressure responsive surface on said stem portion, and a third, oppositely directed pressure responsive surface being defined by said separate stem member, the respective areas being selected so that the second pressure responsive area is substantially equal to the area of the third pressure responsive surface, said second and third surfaces being exposed to system pressure upon opening of said control valve whereby the force produced by said second pressure responsive area is opposed and nullied byl the force produced by the said third pressure responsive area, a spring associated with said' control valve and urgingsaid control valve toward closed position with a predetermined pressure, said control valve when opening tending to compress said spring, the nullitication of said second and third surfaces allowing said spring to oppose only said rst pressure responsive area, supporting means associated with one end of said spring and mounted on said housing whereby the location of said one end of said spring may be pre- 8f determined, and supporting means connected with the other end of said spring and movable in response to movement of said piston whereby the workingv length of said spring is maintained substantially constant despite opening of the said control valve.

3,. A relief valve assembly for a hydraulic systern including a housing having an inlet port, an outlet, port and a chamber interconnecting said ports a relief valve positioned in said chamber and effective when seated to prevent communication between said ports', a piston connected with said relief valve and effective in response to application of system pressure to a motive surface thereof to open said relief valve, a control valve connected with said piston andexposed to system pressure for controlling application of system pressure to said piston, said control valve being movable to open position to apply system pressure to said piston, said control valve including a stem portion and a separate stem member bearing against an end of said stem portion, a rst pressure responsive surface being dened by the control valve portion exposed to system pressure, a second pressure responsive surface on said stein portion and subject toV inlet pressure for directing a force in a direction urging said valve towards open position, and a separatev member connected to said stem member Ihaving a third pressure responsive surface subject to inlet pressure and oppositely directed` relative to saidsecond pressure responsive surface, the eective force of which is defined by said separate stem member for urging said control valve toward closed position, the ei'ective areas of said second and third surfaces. being equal.

References, Cited in the leof this patent UNITED STATES PATENTS Number Name Date 108,345 Goll Oct. 18, 1870 140,194 Hague June 2li, 1873 7153707 Tippett Dec. 9, 1902 1,262,355 Kiesel Apr. 9, 1913 V2,122,706. Armstrong July 5, 1938 

